Automatic electric circuit breakers, particularly those designed for industrial applications, are increasingly being equipped with electronic or solid state trip units in lieu of the traditional thermal-magnetic and dual magnetic trip units. These solid state trip units monitor the line current or currents and automatically initiate circuit interruption in response to abnormal line current magnitudes caused by overload and short circuit conditions. Recently, to satisfy demand, solid state trip units have been supplemented to also provide ground fault protection.
With such multi-function trip unit capability, it would be most desirable to know, from a trouble-shooting standpoint, which one of these trip unit functions was responsible for tripping the circuit breaker and clearing the circuit. Specifically, is the problem to be rectified before power can be restored before power can be restored an overload, a short circuit or a ground fault condition? A positive indication of which problem precipitated tripping of the circuit breaker can greatly simplify the search for the problem source and thus corrective action can be taken all the sooner. In industrial applications, loss of electrical power typically means the curtailment or complete halt in production, which is expensive. Thus, it is highly desirable that a power outage, when it does occur, be held to as short a duration as possible.
It is accordingly an object of the present invention to provide an improved multi-function solid state trip unit for automatic electric circuit breakers.
An additional object of the invention is to provide a solid state trip unit of the above character, which includes indicator means for signaling which of the trip units was responsible for tripping the circuit breaker.
Still another object is to provide a solid state trip unit of the above character, wherein the indicating means is operated off the trip unit power supply.
A further object is to provide a trip unit of the above character which further includes means bypassing the indicating means to insure that the completion of a trip unit function is not jeopardized by failure of the indicating means.
Other objects of the invention will in part be obvious and in part appear hereinafter.